[BOLT] Create section symbols for inserted sections

[yota9]

Summary

Just for consistensy create section symbols for inserted
sections (sections without reference).

Vladislav Khmelevsky,
Advanced Software Technology Lab, Huawei

[Amir]

I'm testing it internally, will get back to it tomorrow

[Amir]

Why do we need to create symbols for these sections?

bolt/lib/Rewrite/RewriteInstance.cpp

5184–5187

bolt/test/create_section_symbol.c

1

bolt/lib/Rewrite/RewriteInstance.cpp

if (Symbol.isAbsolute() || !Symbol.isDefined())
       return false;
 
     // If we cannot link the symbol to a section, leave it as is.
     Expected<const typename ELFT::Shdr *> Section =
         Obj.getSection(Symbol.st_shndx);
     if (!Section)
       return false;
 
-    // Remove the section symbol iif the corresponding section was stripped.
+    // Remove the section symbol if the corresponding section was stripped.
     if (Symbol.getType() == ELF::STT_SECTION) {
       if (!getNewSectionIndex(Symbol.st_shndx))
         return true;
       return false;
     }
 
     // Symbols in non-allocatable sections are typically remnants of relocations
     // emitted under "-emit-relocs" linker option. Delete those as we delete
if (opts::HotText && !NumHotTextSymsUpdated) {
     addSymbol("__hot_end");
   }
 
   if (opts::HotData && !NumHotDataSymsUpdated) {
     addSymbol("__hot_data_start");
     addSymbol("__hot_data_end");
   }
 
+  auto addSectionSymbol = [&](uint64_t Address, unsigned Index) {
+    ELFSymTy Symbol;
+    Symbol.st_value = Address;
+    Symbol.st_shndx = Index;
+    Symbol.st_name = AddToStrTab("");
+    Symbol.st_size = 0;
+    Symbol.st_other = 0;
+    Symbol.setBindingAndType(ELF::STB_LOCAL, ELF::STT_SECTION);
+    Symbols.emplace_back(Symbol);
+  };
+
+  for (BinarySection &Section : BC->allocatableSections()) {
+    if (Section.hasSectionRef())
+      continue;
+
+    addSectionSymbol(Section.getOutputAddress(), Section.getIndex());
+  }
+
   // Put local symbols at the beginning.
   llvm::stable_sort(Symbols, [](const ELFSymTy &A, const ELFSymTy &B) {
     if (A.getBinding() == ELF::STB_LOCAL && B.getBinding() != ELF::STB_LOCAL)
       return true;
     return false;
   });
 
   for (const ELFSymTy &Symbol : Symbols)

bolt/test/create_section_symbol.c

+// This test check that newely created text section would have STT_SECTION type
+// symbol in symtab.
+
+// RUN: %clang %cflags -nostdlib -Wl,-q %s -o %t.exe
+// RUN: llvm-bolt %t.exe -o %t.bolt
+// RUN: llvm-readelf -SsW %t.bolt | FileCheck %s
+
+// CHECK: [[#%x,NUM:]]] .text PROGBITS [[#%x,ADDR:]]
+// CHECK: {{0*}}[[#ADDR]] 0 SECTION LOCAL  DEFAULT [[#NUM]] .text
+
+__attribute__((noinline)) int foo() { return 0; }
+
+void _start() { foo(); }